This invention relates to optical fibre star couplers.
In a conventional star coupler the power in a signal applied to the coupler via a single optical fibre is shared substantially equally between the members of a set of output fibres, this sharing being effected by means of a mixer element interposed optically between the input and output fibres. In a "transmissive" type star coupler one or more input fibres are terminated butted against one end of the mixer element while the set of output fibres have their ends butted against the other end of the mixer element. In a "reflective" type of star coupler all the fibres, both input and output, terminate butted against one end of the mixer element whose opposite end is designed to be totally reflecting. Thus in the transmissive type star coupler optical power input to the coupler on any single one of a first set of (input) fibres is shared substantially equally between the members of a second set of (output) fibres, whereas in the reflective type of coupler optical power input to the coupler on any one of a set of fibres is shared substantially equally between all members of that same set of fibres.
When star couplers are used in large networks that require the input signal to be shared by the coupler between a large number of output fibres it is evident that the amount of power available for any single output fibre is going to be very low if the input signal power is not going to be correspondingly very high. The use of very high power optical transmitters is however undesirable because it presents a potential optical safety hazard should connectors in the optical path between the source and the star coupler become uncoupled.